In another medium bowl, mix the ricotta, eggs, and ½ teaspoon each of salt and pepper to blend. Set aside. Spread the butter over a 13×9-inch baking dish. Spoon one third of the béchamel-marinara sauce over the bottom of the dish. Arrange 5 lasagna noodles atop the sauce, overlapping slightly and covering the bottom of the dish completely. Spread the ricotta mixture evenly over the noodles. Top with the spinach. Arrange 5 more lasagna noodles atop the spinach, then top with the ground beef. Spoon one third of the remaining béchamel-marinara sauce over, then sprinkle with ½ cup of mozzarella cheese. Top with the remaining 5 sheets of lasagna noodles. Spoon the remaining béchamel-marinara sauce over the lasagna noodles, then sprinkle with the remaining mozzarella cheese and the Parmesan cheese. (The lasagna can be made up to this point 1 day ahead. Cover tightly with plastic wrap and refrigerate. Uncover before baking.)